1. Field of the Invention
The present invention relates to a thin film transistor substrate and a method of manufacturing the thin film transistor substrate, and more particularly to a thin film transistor substrate which controls a display of a display device and a method of manufacturing the thin film transistor substrate.
2. Description of the Related Art
As one of display devices for information communication terminals such as computers or for television receiver sets, a liquid crystal display device has been popularly used. The liquid crystal display device is a device which is configured to control an image to be displayed by changing the degree of optical transmissivity with a control of orientation of liquid crystal composition sealed between a thin film transistor substrate (hereinafter referred to as “TFT substrate”) and a color filter substrate.
The TFT substrate used in such a liquid crystal display device has pixels number of which corresponds to the resolution of an image, and each pixel includes a transistor for applying a voltage of a video signal to an electrode. Each layer for forming the transistor such as gate layer, semiconductor layer and source/drain layer is formed by a photolithography step which is a known semiconductor process. In this step, in performing the exposure of a pattern of each layer, it is necessary to perform the alignment for aligning a layer with the previously formed layer.
JP 2007-17465 A (related US patent application: US2007/0009813A1) discloses a technique where an alignment mark is provided for every layer such as a source line layer or a gate line layer of a TFT substrate, and the alignment mark is used at the time of superposing the TFT substrate and a color filter substrate on each other.
JP 1-154124 A discloses an alignment mark which is formed within a display region of a TFT substrate as an alignment mark used at the time of forming respective layers.